1. Field of the Invention
The present invention relates to a method for forming a pattern, a method for manufacturing a semiconductor device, and a semiconductor device, and, in particular, relates to a method for forming an electrically conductive pattern, a method for manufacturing a thin film transistor using the method for forming the electrically conductive pattern, and a thin film transistor.
2. Description of the Related Art
In the field of manufacturing semiconductor devices and image displays such as liquid crystal displays, many kinds of electrically conductive materials are used to form circuits. Since the density and definition have been further increased in recent years in the field of such applications, high resolution and high reliability are desired in a method for forming wiring patterns and an electric conductive material.
In the field of manufacturing electrode substrates to be mounted on electric/electronic components, when a high resolution for forming a circuit pattern on a predetermined substrate is desired, photolithography has been frequently used.
Usually, a circuit pattern is formed by photolithography including depositing an electrically conductive film on a substrate by sputtering or the like, forming a resist film (photosensitive resin) on the electrically conductive film, exposing and developing the resist film to form a resist pattern, and then removing unnecessary exposed portions of the electrically conductive film to form the resist pattern by etching using the resist pattern as a mask. Then, the desired circuit pattern is completed by removing the resist pattern. By using photolithography as mentioned above, very fine circuit patterns can be formed with high resolution.
However, photolithography including steps of exposing, developing, and drying has many steps and is complicated, and it also may need high-precision equipment and environmental control, and a system comes to be large.
Furthermore, when an electrically conductive film is deposited by sputtering, since a high temperature process is desired as a film forming condition, thermal expansion or degradation of the substrate will occur due to thermal stress arising in the substrate. Therefore, when a circuit pattern is formed on a substrate by photolithography, the selection of substrates that can be used is highly limited. Furthermore, in the above-mentioned etching, if a wet etching is used, since the substrate is immersed in an etching solution, the substrate and portions such as a layer under a metal layer having been formed in preceding processes may be damaged.
In consideration of the above, as a method for forming a fine pattern without using photolithography, Japanese Unexamined Patent Application Publication No. 11-58921 discloses a printing method in which a fine pattern is formed by applying ink (resin) onto the entirety of a surface of a first plate, which is called a blanket covered with a silicone rubber, so as to form a thin film, pressing a second plate having a concave-convex pattern on a surface thereof on a surface of the first plate having the thin film formed thereon so as to transfer an unnecessary pattern of the thin film onto top faces of convex portions of the second plate resulting in removal an unnecessary pattern, and transferring the resulting thin film (resin pattern) remaining on the surface of the first plate onto a transfer substrate.
Japanese Unexamined Patent Application Publication No. 2006-278845 discloses another method for forming an electrically conductive pattern, in which an electrically conductive ink composition including metal particles, an aqueous solvent, and a water-soluble resin is used in the printing method described in the Japanese Unexamined Patent Application Publication No. 11-58921.
Note that when the above-mentioned printing method is applied to formation of a circuit pattern of a semiconductor device, the circuit pattern is desired to be 500 nm or less in thickness because a thin circuit pattern is suitable for a thin electronic apparatus. Therefore, it is desired to reduce the thickness of the electrically conductive film applied onto the first plate.